The present invention relates to the field of needled textile structures and it relates more particularly to a system for automatically controlling the spreading of tows that are to form such textile structures.
In traditional industrial needling processes, the textile sheet which is to be needled and which is to be used for example in making protective parts for use at high temperatures, is made up from a plurality of tows placed side by side and each comprising a multitude of textile yarns advantageously of the monofilament type. Each tow comes from a device known as a creeling frame and it exits over a width and at a position that ought, a priori, to enable distribution to be as uniform as possible within the sheet (also referred to as a tow web).
At present, this distribution is provided purely manually by an operator located at the outlet from the creeling frame, with the operator constantly watching the sheet, particularly where tows overlap, and wherever possible manually altering the way it is spread so as to limit imperfections. Unfortunately, when such imperfections are found to be excessive, the process must be interrupted and that gives rise to severe consequences. In addition to the method being particularly expensive in terms of labor costs (particularly if the process is to be performed 24 hours a day), it is not free from defects due to the presence of the human factor.
The present invention mitigates those drawbacks by proposing apparatus for automatically controlling the spreading of a textile sheet made up of a plurality of tows coming from a tow feed module for feeding to a drive module, the apparatus comprising means for measuring the positions of the longitudinal edges of each tow, means for individually adjusting the width of each tow, means for individually adjusting the position of each tow in a direction perpendicular to a tow advance direction, and digital processor means responsive to said position measuring means to control said adjustment means in such a manner that said textile sheet presents determined width and position.
With this particular configuration, it is possible automatically to obtain uniform distribution of the textile sheet whose width and position are thus completely guaranteed and controlled in real time so as to enable it to be introduced into a pre-needling module or directly into a cross-layer.
Advantageously, the means for measuring the positions of the longitudinal edges of each tow comprise either a digital camera placed over the textile sheet or else a detector, preferably a linear optical sensor made up of a plurality of light-emitting diodes placed in register with a plurality of light-receiving diodes with the tow to be measured passing between them. Likewise, the means for individually adjusting the width of each tow comprise a curved adjustment bar which is pivoted about a pivot axis under drive from a first actuator, thereby altering the position of the curve in its central portion which has the effect of acting on the width of the tow passing over said curved adjustment bar. Similarly, the means for individually adjusting the position of each tow in a direction perpendicular to a tow-advance direction comprise a second actuator acting on a bell crank and a connecting rod to move a slider supporting the tow. The first and second actuators are preferably electrically-controlled actuators that are actuated directly by said digital processor means.
The digital processor means comprise a microcomputer or a programmable controller which, on the basis of said measurements picked up by said position detector, controls said first and second actuators to adjust the width and the position of each tow so as to ensure that the width and the position of said textile sheet are regulated relative to predetermined reference values. Advantageously, these predetermined reference values comprise the total width Nc of the sheet, the nominal overlap between tows R1c, R2c, R3c, and the width Lc of an individual tow. Nevertheless, only the referenced values relating to said total width of the sheet and to said nominal overlap are supplied to said digital processor means by an operator, while the reference value relating to the width of an individual tow is calculated automatically by said processor means on the basis of said reference values that are supplied by an operator.
The invention also provides a method of implementing this apparatus for automatically controlling the spreading of a textile sheet.